1. Field of the Invention
The present invention relates to a lens device and, more particularly, to a lens device mounted on a miniature precision apparatus, such as a digital camera and a portable telephone.
2. Description of the Related Art
There is an actuator that uses a piezoelectric element and that serves as a drive device of a lens part of a digital camera or the like. For example, a drive device disclosed in Japanese Patent No. 2633066 is configured so that a driving shaft is fixed to one side of the piezoelectric element and that the other side of the piezoelectric element is fixed to a device body. A lens-barrel is slidably supported by the driving shaft. The lens-barrel is frictionally engaged with the driving shaft by utilizing a pushing force of a leaf spring. A driving pulse having a substantially sawtooth-like waveform is applied to the piezoelectric element. The piezoelectric element deforms in an expanding direction and in a contracting direction at different speeds. For example, in a case where the piezoelectric element gradually deforms, the lens-barrel moves together with the driving shaft. Conversely, in a case where the piezoelectric element deforms fast, the lens-barrel remains at the same position by the inertia of the mass thereof. Thus, the lens-barrel can intermittently be moved at a fine pitch by iteratively applying the driving pulse having the substantially sawtooth-like waveform to the piezoelectric element.
The drive device disclosed in Japanese Patent No. 2633066 is configured so that the driving shaft is directly fitted into the lens-barrel. Consequently, the replacement of a component of the drive device cannot be achieved unless the drive device is completely disassembled. Thus, an actuator disclosed in Japanese Patent No. 3170999 is configured so that a slider is frictionally engaged with a driving shaft, and that a lens-barrel is fixed to this slider. Therefore, the lens-barrel and the actuator can be disengaged from each other. The replacement of a component can easily be achieved.
Meanwhile, each of the related drive devices respectively disclosed in Japanese Patent No. 2633066 and Japanese Patent No. 3170999 is configured so that the entire load due to the lens-barrel is applied to the driving shaft of the actuator. For example, the drive device disclosed in Japanese Patent No. 3170999 is adapted so that the load due to the lens-barrel is supported only by the driving shaft. Also, the drive device disclosed in Japanese Patent No. 2633066 is adapted so that although the lens-barrel is engaged with a guide bar to prevent the lens-barrel from turning, the load due to the lens-barrel is received by the driving shaft. Accordingly, there is a fear that when each of the drive devices respectively disclosed in Japanese Patent No. 2633066 and Japanese Patent No. 3170999 suffers an impact due to the dropping thereof, a large load may be applied to the driving shaft to thereby damage or distort the driving shaft. To solve this problem, it is necessary to thicken the driving shaft to increase the stiffness thereof. However, in a case where the driving shaft is thickened, the piezoelectric element is slow to react. Thus, the related drive devices have problems that the lens-barrel cannot be moved with high precision, and that the size of the device is increased.